This invention relates to scanning nonplanar originals, such as bound books or other three dimensional objects.
Input scanners are widely used for producing digital versions of images on substrates. Digital versions are beneficial because they can be stored, processed, transmitted, and subsequently used by other devices, such as computers, copiers, and facsimile machines.
Input scanners usually include a flat, transparent platen that supports a substrate having an image that is to be digitized, and a moving raster scanner having a light source that radiates a narrow xe2x80x9cstripxe2x80x9d of light through the platen and onto the substrate. Part of that light is reflected by the image on the substrate and collected and focused by the raster scanner""s input optics onto an elongated light sensor array. The light sensor then converts its received light into digital signals that are then stored. As the raster scanner moves across the substrate the light sweeps over the substrate and other light strips are digitized. When the substrate""s image has been completely scanned the digital signals of all of the scan lines represent a digital image.
Scanning three-dimensional (non-planar) substrates such as bound books presents problems. One set of problems relates to defocusing of the image as the raster scanner moves. For example, when scanning a book the book""s pages near the binding tends to become defocused as the pages lift off the platen. This is a particularly acute problem when the input optical system uses gradient index lens arrays. This is because while gradient index lenses are radiometrically efficient, they tend to have a limited depth-of-focus. Outside of the focus range the image is so distorted that it produces a seriously degraded reproduction. For example, some input scanners that use gradient index lens arrays can become significantly defocused by a separation of as little as 1 millimeter.
Various approaches have been used in the prior art to reduce the problems related to scanning three-dimensional objects. With books, one approach is to use xe2x80x9cbrute forcexe2x80x9d to press the book against the platen, thereby reducing the book""s lift. However, portions of the book""s pages still remain above the platen""s surface. Moreover, pressing a book against a flat platen can degrade the book""s binding, especially with older books. Another approach is to use a wedged platen to reduce binding degradation. However, wedged platens tend to reduce overall machine utility and increase cost.
Other approaches are described in U.S. Pat. No. 4,980,720, which issued on Dec. 25, 1990, and which is entitled, xe2x80x9cDocument Reproduction Machine with Enhanced Book Copying Capability,xe2x80x9d and in U.S. Pat. No. 5,276,530, which issued on Jan. 4, 1994, and which is entitled xe2x80x9cDocument reproduction machine with electronically enhanced book copying capability.xe2x80x9d Those patents discuss reproduction machines having a height sensor that determines the distance between a reference point (which may be in the object plane) and an original being scanned. The height information is used to control the position of a scanning mirror that adjusts the focus, illumination, and scan rate. Furthermore, those patents teach using information from a height sensor as an input to an electronic correction circuit that electronically corrects for defocusing caused by height variations. However, those patents discussed adjusting a moving scanning mirror to correct for defocusing. Furthermore, that scanning mirror was only optically coupled to a stationary single lens. Finally, those patents do not involve digitizing an image being scanned, but rather they simply imaged onto a photoreceptor. Therefore, those patents could make use of a relatively long optical path length to assist in focusing. However, with the advent of digital scanners, elements such as gradient index lens arrays, elongated sensor arrays, short optical path lengths, and mirrors disposed between gradient index lens arrays and elongated sensor arrays became common. Therefore, a new approach to copying three-dimensional objects on a flat platen would be beneficial.
The principles of the present invention provide for improved scanning of a three-dimensional object placed on a platen. An input scanner according to the principles of the present invention includes a platen that supports a three-dimensional object that is to be scanned, a raster scanner that produces a digital representation of the image on that object, and a mechanism that moves the raster scanner across the platen. The raster scanner includes a moving carriage, a light source on the moving carriage, an elongated sensor array, an optical system, and a positioning system. The light source emits a narrow line of light through the platen. The optical system, which includes a mirror and at least one lens array, focuses light from an object plane onto the elongated sensor array. The elongated sensor array then produces a digital representation of a line image in the object plane. The positioning system adjusts the object distance as the raster scanner moves across the platen such that the object plane tracks the contour of the three-dimensional object on the platen.
Object plane adjustments are performed by moving the mirror. A lens array might also be moved. The positioning system follows a contour matching system, which may be a mechanical track guide, a profile memory, or a height sensor.